Diesel engine use for passenger car applications is increasing due to the benefit of better fuel economy. Further, gasoline engines are increasing compression ratios to improve the fuel efficiency. As a result, diesel and gasoline engine accessory drive systems have to overcome the vibrations of greater magnitude from crankshafts due to above mentioned changes in engines.
Due to increased crankshaft vibration plus high acceleration/deceleration rates and high alternator inertia the engine accessory drive system is often experiencing belt chirp noise due to belt slip. This will also reduce the belt operating life.
Crankshaft isolators/decouplers and alternator decouplers/isolators have been widely used for engines with high angular vibration to filter out vibration in engine operation speed range and to also control belt chirp.
Representative of the art is U.S. Pat. No. 8,931,610 which discloses an isolator decoupler comprising a pulley, a shaft, the pulley journalled to the shaft on a low friction bushing, a spring carrier, the pulley journalled to the spring carrier on a low friction bushing, the spring carrier journalled to the shaft on a low friction bushing, a torsion spring coupled between the pulley and the spring carrier, a one way clutch spring frictionally engaged with the shaft, the one way clutch spring coupled to the spring carrier, the one way clutch spring is disposed radially inward of the torsion spring, and the pulley temporarily engagable with an end of the one way clutch spring whereby the frictional engagement of the one way clutch spring with the shaft is temporarily diminished.
What is needed is an isolating decoupler having a torsion spring having a first section having a major diameter and a second section having a minor diameter, the second section is disposed radially outboard of a wrap spring such that the second section moves radially inward to progressively clamp the wrap spring to a shaft during a load condition. The present invention meets this need.